The coal-water slurries reported in the patent and open literature for the most part have particle size distributions of 60-80 percent .+-.200 mesh (74 .mu.m).times.0 and ash contents of 3+ to over 10 wt percent. Such mixtures are described in U.S. Pat. Nos. 3,517,628 issued June 30, 1970, to H. Harnisch et al; 3,682,114 issued Aug. 8, 1972, to F. Scheubel et al; 3,762,887 issued Oct. 2, 1973, to Clancey et al; 3,764,547 issued Oct. 9, 1973, to Schlinger et al; 4,282,006 issued Aug. 4, 1981, to J. Funk; and 4,304,572 issued Dec. 8, 1981, to H. Wiese et al and in the following papers, all presented at the 4th International Symposium on Coal Slurry Composition, Orlando, Fla., May 10-12, 1982: K. Aoki et al, Pretreatment of Coal for Coal Water Slurries, Sumitomo Heavy Industries, Ltd.; R. Borio et al, Coal-Oil Mixture and Coal-Water Mixture Fuels for Steam Generators, Combustion Engineering, Inc.; G. Germane et al, Coal-Water Mixture Combustion Studies in a Laboratory Cylindrical Combustor, Combustion Laboratory, Brigham Young University; M. Ghassemzadeh et al, Rheology and Combustion Characteristics of Coal-Water Mixtures, Babcock and Wilcox Company; and R. Scheffee et al, Further Development of and Evaluation of Coal-Water Mixture Technology, Atlantic Research Corporation.
The Borio et al paper does refer to one slurried coal--identified as super clean beneficiated--that reportedly has an ash content of 1.1 wt. %. However, that is not on a moisture-free basis, meaning that the ash content of the coal on that basis is over two wt. %.
Furthermore, the seam from which the raw coal was mined is not identified. Consequently, the reported ash content of the product coal may or may not be particularly notable.
Also of importance is that the particle size distribution of the coal in the slurry described by Borio is only 85% 44 .mu.m.times.0. As a consequence, the substitution of that slurry for the existing fuel in an electrical generating unit, for example, would be apt to require extensive--and correspondingly expensive--retrofit of the steam generator; and a significant derating of the generator might result.